Coated columbium article



Aug- 3, 1965 w. B. HALL 3,198,653

COATED GOLUMBIUM ARTICLE Filed Aug. 2, 1962 United States Patent Officey Patented Aug. 3, i965 This invention relates generally to a coatedarticle and a method for preparing the same. More particularly, thisinvention is concerned with providing protection for columbium andcolumbium alloys against oxidative degradation at high temperatures.

High speed jet aircraft engines, especially in the afterburner section,achieve temperatures in excess of that which normally causes oxidationof columbium metal when such metal is exposed to an oxidizing atmospherethereby precluding the utilization of the refractory characteristics ofthis metal in such applications. In addition, the high temperatures injet aircraft engines causes minute amounts of gas to diffuse into themetal thereby causing severe embrittlernent defects.

The `solutions to the aforementioned problems `are provided by thisinvention in order to allow for the utilization of refractory metalcolumbium, with its high melting point, in the construction of jetengines and turbines.

In addition, a simple, easily produced coated article is provided whichhas utility in jet afterburner linings, 'turbine blades, etc., orwherever a refractory metal is subjected to high temperatures duringuse. The coating of this invention provides a coated base which issubstantially resistant to thermal shock, gas embrittlement andoxidative degradation.

Columbium is a refractory metal having a melting point of 4380" F.;however, exposure to temperatures of about 1000 F. in an oxidizingatmosphere causes severe oxidation of the metal and diffusion of gasinto the metal thereby causing embrittlement.

To overcome this problem a structure of columbium or `one of its alloysis provided with a first coating of alumina and a second coating of aslip sprayed glasslike metal oxide which protects the metal fromcontamination and oxidation up to a temperature of 2500 F. The drawingillustrates the coated article of this invention and the best method ofcarrying the invention into effect.

In the drawings:

FIGURE 1 is an isometric View in cross-section and exploded form of thecoated oclumbium base of this invention; and

FIGURE 2 is a ow lsheet diagram showing the various process stepsinvolved in the production of the coated article of FIGURE 1.

In order to coat columbium or its alloys, the metallic structure mustrst be cleaned, for example, by grit blasting. A ten mil layer ofalumina is then deposited onV that portion of the surface to which wouldbe exposed to high temperature conditions in an oxidizing atmosphere.Flame spraying of alumina is the method chosen for applying the coatingWhile alumina is utilized because of its inertness with respect tocolumbium and, with ilame spraying, provides superior adherence tocolumbium.

A glass-like metal oxide which forms the `second coating is slip sprayedover the alumina and tired in a purified argon atmosphere. The metaloxides utilized in accordance with the teachings of this invention areselected from the group consisting of MgO, BaO, and SiO2.

A columbium alloy article coated by the above-described method providesconstant protection of the base metal from oxidation and contaminationfor 200 hours at a temperature of 2300 F. Testing further indicated thatno failure due to thermal shock of thermal cycles of 1000 F. to 2300 F.in two minute cycles occurs to the coating.

Thus, the coated columbium or columbium alloy articles describedprovides protection for a longer period of time by means of a single,low cost process against the deleterious effects to which refractorymaterials are subjected at high temperatures.

Although the invention has been described with reference to a particularembodiment, it will be understood to those skilled in the art that theinvention is capable of a variety of alternative embodiments within thespirit and scope of the appended claims.

I claim:

1. A coated metal article comprising a base of columbium metal, a firstlayer of llame sprayed alumina bonded to said base and a second layer ofa fired, slip sprayed metallic oxide bonded to said first layer in whichsaid metallic oxide is selected from the group consisting of MgO, BaO,and SiO2.

2. A coated metal article in accordance with claim 1 wherein said secondlayer is MgO.

3. A coated metal article in accordance with claim 1 wherein said secondlayer is BaO.

4. A coated metal article in accordance with claim 1 wherein said secondlayer is Si02.

References Cited by the Examiner UNITED STATES PATENTS 3,038,817 6/62Day et al 117-70 X 3,054,694 9/ 62 Aves 117-46 X 3,057,048 10/ 62Hirakis 29-194 FOREIGN PATENTS 895,848 11/53 Germany.

RICHARD D. NEVIUS, Primary Examiner.

WILLIAM D. MARTIN, Examiner.

1. A COATED METAL ARTICLE COMPRISING A BASE OF COLUMBIUM METAL, A FIRSTLAYER OF FLAME SPRAYED ALUMINA BONDED TO SAID BASE AND A SECOND LAYER OFA FIRED, SLIP SPRAYED METALLIC OXIDE BONDED TO SAID FIRST LAYER IN WHICHSAID METALLIC XIDE IS SELECTED FROM THE GROUP CONSISTING OF MGO, BAO,AND SIO2.